Journal Article
Title | Ligand binding and signalling pathways of PTH receptors in sea bream (Sparus auratus) enterocytes. |
Publication Type | Journal Article |
Authors | Rotllant, J, Guerreiro, PM, Redruello, B, Fernandes, H, Apolónia, L, Anjos, L, Canario, AVM, Power, DM |
Year of Publication | 2006 |
Journal | Cell Tissue Res |
Volume | 323 |
Issue | 2 |
Date Published | 2006 Feb |
Pagination | 333-41 |
ISSN | 0302-766X |
Keywords | Amino Acid Sequence, Animals, Binding Sites, Calcium Signaling, Cyclic AMP, Enterocytes, Gene Expression, Ligands, Molecular Sequence Data, Parathyroid Hormone-Related Protein, Receptor, Parathyroid Hormone, Type 1, Reverse Transcriptase Polymerase Chain Reaction, RNA, Messenger, Sea Bream, Sequence Homology, Amino Acid, Takifugu, Zebrafish |
Abstract | Whole animal studies have indicated that Ca(2+) uptake by the gastrointestinal tract is regulated by the action of parathyroid hormone-related peptide (PTHrP) in teleost fish. We have characterised PTH receptors (PTHR) in piscine enterocytes and established, by using amino-terminal PTHrP peptides, the amino acid residues important for receptor activation and for stabilising the ligand/receptor complex. Ligand binding of (125)I-(1-35(tyr)) PTHrP to the membrane fraction of isolated sea bream enterocytes revealed the existence of a single saturable high-affinity receptor (K (D)=2.59 nM; B (max)=71 fmol/mg protein). Reverse transcription/polymerase chain reaction with specific primers for sea bream PTH1R and PTH3R confirmed the mRNA expression of only the later receptor. Fugu (1-34)PTHrP increased cAMP levels in enterocytes but had no effect on total inositol phosphate accumulation. The amino-terminal peptides (2-34)PTHrP, (3-34)PTHrP and (7-34)PTHrP bound efficiently to the receptor but were severely defective in stimulating cAMP in enterocyte cells indicating that the first six residues of piscine (1-34)PTHrP, although not important for receptor binding, are essential for activation of the adenylate cyclase/phosphokinase A (AC-PKA)-receptor-coupled intracellular signalling pathway. Therefore, PTHrP in teleosts acts on the gastrointestinal tract through PTH3R and the AC-PKA intracellular signalling pathway and might regulate Ca(2+) uptake at this site. Ligand-receptor binding and activity throughout the vertebrates appears to be allocated to the same amino acid residues of the amino-terminal domain of the PTHrP molecule. |
DOI | 10.1007/s00441-005-0070-7 |
Sapientia | |
Alternate Journal | Cell Tissue Res. |
PubMed ID | 16189716 |